lewis



Tan. 24, 1955 F. M. LEWIS STARTER FOR FREE PISTON GAS GENERATOR Filed Aug. 9. 1954 INVENTOR FRANK M. LEWIS ATTORNEYS United States PatentO 2,731,793 STARTER FOR FREE PlSTON GAS GENERATOR Frank M. Lewis, Weston, Mass, assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application August 9, 1954, Serial No. 448,788

4 Claims. (Cl. 60-14) This invention relates to a starter for a free piston gas generator and more particularly to a starter for a free piston gas generator of the internal combustion type.

Starters for free piston gas generators of the internal combustion type must properly orient the free engine pistons and must force the engine pistons through a compression stroke to compress air in the power cylinder to the pressure and temperature required to ignite the fuel injected therein. The starter must also provide reliable starting with varying initial conditions of temperature, pressure and orientation of the free pistons and must be simple to operate so that the gas generators may be started by unskilled personnel.

It is an object of this invention to provide a novel and improved starter for a free piston gas generator of the internal combustion type.

Another object of this invention is to provide a novel and improved starter for a free piston gas generator of the internal combustion type, which starter is reliable and efiicient in its operation and simple in its control.

Other objects and advantages of the invention will hereinafter become more fully apparent from the following description of the annexed drawing, which illustrates a preferred embodiment, and wherein:

The single figure of the drawing is an elevationalview, partially in section, of a free piston gas generator of the internal combustion type incorporating the starter of this invention, the starter and controls therefor being shown exaggerated in size for clarity.

Description Referring now to the drawing, the reference numeral designates the housing of a free piston gas generator of the internal combustion type, similar to the one described in the patent to F. M. Lewis, et al., 2,600,251, entitled Starter for Free Piston Engine, and which comprises a central power cylinder 13, a pair of larger combination cylinders which are at opposite ends of the power cylinder 13 and coaxial therewith, and a pair of direct bounce cylinders 17 which are coaxial with the power and combination cylinders 13 and 15 and are located at the outer extremities of the housing 10. A pair of opposed engine pistons 11 and 12' are positioned in the power cylinder 13 to reciprocate therein, and each piston 11 or 12 comprises one piston of a group of pistons termed a piston unit. Each of the piston units further comprises a combination piston 14 which reciprocates in the combination cylinder 15, and a direct bounce piston 16 which reciprocates in the direct bounce cylinder 17. The pistons of each piston unit are directly connected together to form a unitarily operating structure. Only one set of cylinders comprising cylinders 13, 15 and 17, and one piston unit comprising pistons 11, 14 and 16 have been shown in detail. Since both sets and units are identical, the auxiliary equipment to be described in connection with one unit will be understood to have a counter-part for the other unit. l

Adjacent the outer ends of the housing 10 are auxiliary 2,731,793 Patented Jan. 24, 1953 ice air chambers 18 to which compressed air is supplied for starting. The auxiliary air chambers 18 communicate with the direct bounce cylinders 17 through ports 20 which are so positioned that they are covered by the direct bounce pistons 16 in their outermost positions. The pistons 16 have a sufficiently loose fit in the outer ends of the direct bounce cylinders 17 so that when the ports 20 are covered thereby, air under pressure in the auxiliary air chambers 18 is permitted to leak around the ends of the pistons 16 and to enter the direct bounce cylinders 17 in the free spaces provided between the ends of the cylinders 17 and those of the pistons 16. Compressed air is admitted into each auxilary air chamber 18 through a pipe 31 and a pressure regulating valve 32, and the flow of air through the pipe 31 is controlled by a valve 35 which comprises a valve stem 36 and a compression spring 37. Compressed air is supplied to the valve 35 from a compressed air source (not shown) through a supply line 44.

The combination pistons 14 divide each of the combination cylinders 15 into two chambers, a compressor chamber 15a and a reverse bounce chamber 15b. Air is supplied through a pipe 21 to the compressor chambers 15a which are connected together and to the power cylinder 13 by a conduit 22 through which air compressed in the chambers 15a is supplied to the cylinder 13, and high pressure combustion products are exhausted from the power cylinder 13 through an exhaust conduit 27 which is connected to the engine (not shown) to be driven by these gases. A fuel injector 19 injects fuel into the power cylinder 13 at the proper time by means not shown. Compressed air for starting may be supplied to the reverse bounce chambers 15b from the supply line 44, through a pipe 33 and a regulating valve 34, and is controlled by a valve 41 which comprises a valve stem 42 and a compression spring 43. The reverse bounce chambers 15b may be vented to the atmosphere on starting by dump reciprocating valves 23 which comprise valve pistons 24 positioned in valve cylinders 26, and which are biased toward the closed position by springs 25 bearing against the pistons 24. Compressed air to move the pistons 24 against the action of the springs 25 and open the valves 23 may be supplied to the cylinders 26 by a pipe 64, from the supply line 44 through a starting unit 45.

The starting unit 45 comprises a generally cylindrical housing 46 containing a lower compartment 47 communicating with an upper compartment 48 through a valve 53. A small diameter cylinder 50 opens directly into the top of the upper compartment 48 and serves to connect the upper compartment 48 with a large diameter cylinder 52 in the top portion of the housing 45 forming a shoulder 62 therein. The cylinders 50 and 52 are oriented with their longitudinal axes vertical and are coaxial.

A heavy mass 61 is'positioned within the large diameter cylinder 52 to move vertically therein and has a downward extending tubular extension 60 which fits closely within the small diameter cylinder 50. The heavy mass 61 rests upon the shoulder 62 when it is in its downward position. The housing 46 is pierced by ports 63 there'- through in the top portion of the small diameter cylinder 50 just below the shoulder 62, and the ports 63 are covered by the tubular extension 60 when it is in its downward position, and uncovered when it is in its upward position. A stationary disk or piston 59 is positioned in the tubular extension 60 and is secured to the valve 53 in housing 46 by a rod 58, thus'reducing the effective piston area of the lower end of the extension 60. A pipe 51 which includes a pressure regulating valve 49 connects the interior of the lower compartment 47 with the' supply line 44. The pressure regulating valves 32, 34," and 49 are well known in the art and are not described in detail t Ih Pr s u e re u t ng a ve 49 res r ct the ra s.

of flow of air into the housing 46 to an amount less than the amount that can escape through the ports 63 when he are un o r A p pe 6 nn c t e uppe s partrn ent 48 with the cylinders of the fficiprocating valves 23.

Qrre arm 56 of apivoted bell crank 57 bears against an extension 54 of a valve stem 55 of the valve 53 to mainrain that valve normally closed. The bell crank 57 comprises a second arm ,65 which bears against a cam 67 having a sharp step .68. A second cam 65, operatively conpected'to the cam 67 to rotate therewith, has a proinst l s rurt czn or os 7. ar anged to b ar agains n end of a lever'66, and the other end of the lever .66 abuts the top end of the valve stem 42 to controlthe operation of the valve 41, A third cam 72, operativcly connected to the cams 67 and 69 to rotate therewith, has a projecting portion or nose 73 arranged to bear against one end of a second lever 74, and the other end of the lever 74 abuts the top end of the valve stem 36 to control the oPQ ation of the valve 35.

Operation The gas generator is started by first rotating the earns 67, 69,-and 72 until the nose 71 on the cam 69 bears against and rotates the lever 66 to open the valve 41 and admit compressed air from the supply line 44 into the reverse bounce chamber b. The pressure of the air admitted to the reverse bounce chamber 15b acts on the piston 14 to move the pistons 11, 14 and 16 in the direction of their outward strokes. The pistonunit comprising the piston 12is moved in a similar manner and its operation will not be further described. Air is forced from the chamber 154: into the power cylinder 13 through the conduit 22 by the movement of the pistons 14.

The cams 67, 69 and 72 are then rotated until the nose 73 of the cam 72 causes the lever 74 to rotate, opening thevalve and admitting compressed air to the auxiliary air chamber 18. The pressure regulating valves 32 and 34 are so adjusted that the pressure of the air in the auxiliary air chamber 18 exerts a slightly lesser force against the piston 16 than the air in the reverse bounce chamber 15b exerts against the piston 14.

;Ater the piston unit has been moved to the end of its ootward stroke by the air in'the chamber 15b and the air pnder pressure in the auxiliary air chamber 18 and in the reverse bounce chamber 15b has become stabilized, the cams'67, 69 and 72 are rotated farther or until the endof thebell crank 57 clears the end of the sharp step 68in the cam 67- removing the impediment to the rotation of the bell crank 57. By this time, the noses 71 and 73 have moved past the levers 66 and 74 and have allowed the valves 35 and 41 to close under the action of the springs 37-.and 43 respectively. The pressure of the air in the lower compartment 47 of the starting unit 45 then jorces the valve 53 open, causing thebell crank 57 to rotate and the end of the arm 65 to fall into the step 68. The compressedair supplied to the housing 46 through the pipe 51 expands throughout the housing 46, exerting an upward force on the lower end of the tubular extension 60 and moving the heavy mass 61 upwardly. The mass 61 moves upwardly under the action of the-pressure oi the air in the upper compartment 48 and in the small diameter cylinder 50 but is retarded in its movement by its own mass which must be accelerated from rest.

Compressed air is conducted from the upper compartmeat 48, through the pipe 64 to the valve cylinder 26 of the dump valve 23, forcing open the dump valve 23 against the action of the spring 25, and allowing the air in the reverse bounce chamber 15!: to vent to the atmosphere. The air in the auxiliary air'chamber 18 must leak around the circumferential clearance of the bounce pisqn 16;;11 the outward position to which it. was moved'by air under pressureinthereverse bounce chamber 15b, hefo're'it can get behind the piston 16 and do work.

ans-tans While thi rela i e sl wcwss s i ak ng P e th air iii pressure in the reverse bounce chamber 15)!) drops to substantially atmospheric pressure, and the piston units 11, 14 and 16 is then forced in the direction of a com pression stroke by the air under pressure in the direct bounce cylinder 17 and the auxiliary air chamber 18.

The dump valve 23 must remain open during the com- Pression stroke of. the engine piston 11 and during the early portion of the succeeding outward stroke so that air may be drawn into the reverse bounce chamber 151; to provide a cushion for the pistons 11, 14 and 16 on subsequent compression strokes. To maintain the dump valve 23 open during this time, the air pressure in the housing 46 must be maintained suflicicntly high to keep open the valve 23 against the action of the spring 25. The pressure of the air in the housing 46 remains high until the ports 63 are uncovered by the tubular extension 61}, at which time the air exhausts through the ports ,63 to the. atmosphere and the air pressure in the housing 4.6 and in the cylinder 26 drops allowing the spring 25 to close the'dump valve '23. The inertia of the mass 61 to which the extension 66 is secured retards the upward movement of the extension 60 for a finite period of time.

Details of construction For a tubular extension 60 of a fixed size and forming a piston .of fixed area at its lower end the speed with which the mass 61 will rise under the infiuenceof the air underpressure in the upper compartment 48 and in the cylinder 50 is determinedby the pressure of the air in thehousing .46 and by the weight of the mass 61. Since the weight of the mass 61 is rather difficult to vary once the starting unit has been constructed, the pres- Sure of the air entering the housing 46 from the supply line 44 is controlled to control the rate of rise of the mass 61 and. the extension 60. The pressure regulating valve 49 isrnade adjustable, and, for proper operation of the starter, is adjusted until the pressure of the air entering the housing 46 from the pipe 51 is sufficient to force the mass 61 upward to the point Where the ports 63 are uncovered by the extension 60 in the time required for the engine piston 11 to complete its compression stroke and that much of its return outward stroke as is necessary to draw sufiicient air into the reverse bounce. chamber 15b to form a cushion for the piston unit on its subsequent compression strokes. In this manner, changes may be made in the time of travel of the weight 61 to compensate for variations in starting conditions ofthe equipment and operation.

In order for the air under pressure to exhaust rapidly from the housing 46 even though air continues to enter thmugh the pipe 51, the aggregate cross-sectional area of the ports 63 must be greater than the cross-sectional area of the pipe 51, the valve 53 or the opening in the pressure regulating valve 49, This necessitates .a comparatively :large diameter cylinder and, since the extension must fit closely in the cylinder 50, it must also be vofi large diameter. To decrease the effective pis ton area at. the lower end of the extension 60, the extensign is made tubular by boring or other means, and the stationary piston 59 is positioned therein.

, The cams .67, 69 and 72 are mounted upon one shaft toxbe rotated together, and for the. proper operation of the equipment, it is preferred that the cams 67, '69 and 71 be angularly displaced around the shaft to eifect the proper sequenceof operations.

The-starter of this invention is simple in its constructipn and operation, yet reliable. It is capable of the precision timing necessary to start free piston gas generators of the internal combustion type, but is easily operated by unskilled operators. The starter will start a free piston, gasgenerator regardless of the initial positions of the-pistons and is adiustableto provide for varying conditions of pressure, temperature-and equipment.

obviously many modification-s and variations on the i present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

l. A starter for an internal combustion engine of the free piston type having a pneumatic direct bounce chamber, the compression of air in which tends to move the engine piston in the direction of its compression stroke, and a pneumatic reverse bounce chamber, the compression of air in which tends to move the engine piston in the direction of its outward stroke, said starter comprising means for injecting air under pressure into said reverse bounce chamber and then into said direct bounce chamber, the air injected into said reverse bounce chamber exerting a greater force than the air injected into said direct bounce chamber to move the engine piston through its outward stroke, an exhaust valve for exhausting said compressed air from said reverse bounce chamber into the atmosphere, means for biasing said exhaust valve to the closed position, mechanism responsive to air pressure for opening said exhaust valve, and timing means for supplying salcl last named air pressure to said mechanism for a predetermined period of time, said timing means comprising an actuating chamber communicating with said mechanism, a conduit for admitting air under pressure to said actuating chamber and to said mechanism to open said exhaust valve, a vertical cylinder having exhaust ports in the upper end thereof, and a weighted piston in said cylinder covering said ports and adapted to be moved upwardly therein for a fixed distance without uncovering said ports and for an additional distance upwardly for uncovering said ports by the air pressure in said actuating chamber, said ports being of sufiicient size to reduce the pressure of the air in said actuating chamber and said mechanism to below the pressure at which said mechanism maintains said exhaust valve in the open position.

2. The starter defined in claim 1 wherein said exhaust valve comprises a reciprocating valve having a stem connected thereto, and said mechanism comprises a cylinder, a piston in said cylinder and adapted to reciprocate therein, said piston being connected to said valve stem to move said reciprocating valve and resilient means in said cy1inder bearing against said valve piston for biasing said reciprocating valve to the closed position whereby the admission of compressed air to said valve cylinder through said conduit moves the piston against the action of said spring to open said valve.

3. The starter defined in claim 2 wherein said weighted piston has an axial bore therethrough, and further including a stationary memberclosely positioned in said bore, whereby the effective piston area of said weighted piston is reduced.

4. A timing device comprising a housing providing a vertical timing cylinder, exhaust ports in the housing communicating with the cylinder, a weighted piston within said cylinder adapted for vertical movement and normally covering said ports, an air chamber within said housing and below the cylinder, a partition in the housing separating the air chamber and the cylinder and having an aperture of less cross sectional area than the aggregate cross sectional area of said exhauts ports, a fluid pressure responsive valve for said aperture, means for supplying air under pressure to the air chamber, releasable holding means for said valve for controlling the flow of air under pressure from the air chamber to the cylinder to force the weighted piston upwardly to uncover the ports, connections for said timing cylinder to receive air under pressure therefrom for an interval of time equal to the time between the opening of said valve and the exhaustion of said air under pressure through the ports to the atmosphere and for releasing said holding means, and means connected to said means for introducing air under pressure into the air chamber to control the pressure of the air so introduced whereby the time of rise of said weighted piston may be regulated.

References Cited in the file of this patent UNITED STATES PATENTS 2,306,978 Pateras Pescara Dec. 29, 1942 2,434,877 Welsh et al. Jan. 20, 1948 2,600,251 Lewis et al. June 10, 1952 2,611,233 Welsh Sept. 23, 1952 2,642,717 Whitney June 23, 1953 2,688,337 Shivers Sept. 7, 1954 

